The present invention relates to a fixing apparatus for copying machines and facsimiles which use toner, and more particularly, it relates to a radiant heat fixing apparatus.
In a conventional copying machine facsimile which uses toner, a recording medium on which toner images are developed by electrostatic force is passed between heat rolls to fuse and fix the toner on the recording medium.
In such a fixing apparatus having heat rolls, when the recording medium comprises recording paper, since the recording paper was heated together with the toner in the fixing process, there arose a problem that the paper curled due to evaporation of moisture in the paper and/or the paper shrunk due to local evaporation of moisture in the paper. Further, there was also a problem that the toner adhered to the heat rolls, thus preventing further effective fixing operations. Further, since the heat rolls cannot be heated to a desired temperature immediately after they are energized, in use, the heat rolls must be maintained in the energized condition so that the toner image on the recording medium can be fixed at any time, this is apparently disadvantageous from the view-point of saving energy.
In order to resolve the above-mentioned disadvantages, a radiant heat fixing apparatus wherein the heating is effected by a flash of a xenon flash lamp has been proposed as disclosed in the Japanese Utility Model Laid-Open No. 52-86429. This conventional fixing apparatus comprises a heating device including a xenon flash lamp, and a plurality of conveyor belts extending through a flash illuminated portion from the heating device. A recording medium on which toner images are developed by electrostatic force is sent, by means of the conveyor belts, into the flash illuminated portion from the heating device, where the recording medium is heated by the flash of the heating device, thus fusing and fixing the toner on the recording medium.
In this conventional fixing apparatus, since only the toner on the recording paper is heated, there is no problem with curling and/or the shrinking of the recording paper. Of course, since heat rolls are not used, there is no problem regarding the adhesion of the toner onto the heat rolls. Further, since the xenon flash lamp can emit the flash at the same time it is energized, the lamp may be energized only when the recording paper to be fixed is in the illuminated portion of the xenon flash lamp, thus saving considerable energy.
However, in this conventional fixing apparatus, it is not considered that the conveyor belts are heated; thus, when the conveyor belts are heated by repeated fixing operations to a temperature greater than the temperature that deforms the recording medium, the latter may be unfavorably curled or shrunk; and, in the worst case, the temperature of the conveyor belts will exceed a firing temperature of the recording medium, resulting in combustion of the latter.
Further, in the above-mentioned conventional fixing apparatus, no consideration is given to thermal expansion of the conveyor belts; thus, when the conveyor belts are heated by repeated fixing operations, there arises slack in the conveyor belt, which may cause the relative slipping or sliding movement between the conveyor belts, and driving rollers by which the belts are entrained, thus causing a problem with the transportation of the recording medium. Further, due to the slack in the conveyor belts, an illuminating angle of the flash with respect to the recording medium may be changed, thus causing a problem of imperfect fixing.
Furthermore, in the above-mentioned conventional fixing apparatus, since it is not considered that foreign matters may be adhered on an outer surfaces of the conveyor belts, if gas emitted from the heated toner adheres to on the outer surfaces of the conveyor belts as an impurity, there arises a problem that the impurity smears the back of the recording medium when it encounters the latter.
Lastly, in the above-mentioned conventional fixing apparatus, since it is also not considered that recording paper is used as the recording medium, there is a problem that paper powder from the recording paper which accumulates on the outer surfaces of the conveyor belts and fired by repeated heating to the belts and also that the paper powder drops through gaps between the conveyor belts to adhere on the back of the lower run of each conveyor belt, thus causing slipping movement of the belts, thereby creating a risk of imperfect transportation of the recording paper such as oblique motion of the paper, reduction of paper speed and the like.